When I was young at Primary 3, my father retired from the Observatory and we moved from the upper room on the 4th floor of 47 Hillwood Road to a flat in Chatham Building of the Hong Kong Chinese Civil Servants' Association at 424 Chatham Road, Hung Hom. In our new home, my father had kept his steel desk and placed it by the window. On the wall next to the desk, there was a square object measuring approximately 6 inches by 6 inches (Figure 1), made up of a wooden frame and two meters. I knew the rectangular meter on the right. People called it, in Cantonese, a "meter showing summer and winter", but its proper name was "thermometer". On either side of a very thin glass tube about four inches long, there were scales marked in degree Celsius and Fahrenheit. At that time, the British system was still in use in Hong Kong and the Observatory reported temperatures in Fahrenheit.
To the left of the thermometer was a larger meter with two "pointers" and some English words on it. Given the fact that I was in Primary 3 and "a man and a pen" pretty much summarised my English proficiency, I had no idea what this meter did.
Figure 1 Mr Heywood, former Observatory's Director, and his wife presented this home thermometer and barometer
as a retirement gift to Mr Lau Pak-wa, the father of Lau Tin-chi.
My father cherished this small piece of instrument that he had hung on the wall. I could not reach the bottom part of it even on tip toe, let alone mess with it. On a typical day, my father would not pay much attention to the instrument, but he would look at it closely during the typhoon season.
I realised that the pointers did not move like the hands of a clock. Normally the pointers stayed quiet, but when a "typhoon is coming", the pointer on the left would move downwards. While people in Hong Kong used to say "typhoon is coming!", fewer and fewer people use the expression in recent years. In the past when there was no air conditioning, people were much more sensitive to temperature changes. On a certain day, it was exceptionally hot and stuffy, even with electric fans and paper fans, and the breeze was hot even in open areas. After dark, there were flying termites everywhere; sometimes, even cockroaches flew, and everyone knew "typhoon is coming!".
In those days, typhoons were a big deal. People were particularly anxious, as if they were facing a formidable enemy. This was because even in concrete buildings, the windows mostly had wooden frames and it was crucial that precautionary measures were taken before a typhoon struck. Wooden windows were secured with ropes and the glass was taped, while window leaks were sealed. It was indeed a lot of work getting prepared for heavy rain or the typhoon. Meanwhile, it was worse for people living in unauthorized rooftop structures, close to a hill or on boats. Everyone hoped that Hong Kong would not be caught in the path of a typhoon, because if it was, homes might be destroyed and lives could be lost. Forty years later in Hong Kong today, people feel completely different about typhoons.
Before the arrival of the typhoon, my father would be busy looking at this small instrument. He would adjust the small silver pointer and observe how the other one moved. A few hours later, if the other pointer moved further downwards, he would announce with absolute certainly that, "the typhoon will hit!" As a kid, I did not understand all the fuss about typhoons. Although I would get an extra day off from school, I would be stuck at home and it was rather boring.
As I grew older, I learnt that the instrument was a barometer. Not requiring any batteries or other power sources, the "mechanics" inside senses the atmospheric pressure and causes the pointers to move. For details of the principle, you need to ask a scientific officer. After my father passed away, I had a good look at this "old friend" that had been in our family for decades. It was given to my father by the then Observatory's Director Mr Heywood and his wife. The names of the givers and receiver, along with the date of presentation, were inscribed on a small plate under the wooden frame. Our "old friend" had served our family since my father's retirement up till his passing, but after I became its owner, it was treated as an ornament on my desk because I did not know how to use it. Therefore, when I met Mr Shun, the current Director, and Ms Song, Senior Scientific Officer, and learned from them that there was a History Room in the Observatory, I offered to send this "old friend" that had been with our family for more than six decades to a place where its existence would be more meaningful (Figure 2). When members of the public visit the History Room, hopefully our "old friend" can show them what a home barometer in the past looks like.
Figure 2 Lau Tin-chi (right) donated his father's retirement gift, a thermometer and barometer, to the Observatory.
Mr Shun Chi-ming, the Director of the Hong Kong Observatory (left), received the instrument from him.
Figure 3 In the early 1950s, Lau Pak-wa (right), the father of Lau Tin-chi, worked in the Hong Kong Observatory.
This photograph shows him with the young Lau Tin-chi sitting on a stone pier at Hong Kong's first
survey station. Today, Lau Tin-chi (left) revisits the place, and he says the giant stone pier has
shrunk. (Photo courtesy of Apple Daily)
Mr Lau Tin-chi
When a tropical cyclone enters within about 800 kilometres of Hong Kong and may affect our territory, the Hong Kong Observatory will issue the Standby Signal No. 1 to remind the public to take timely precautions against strong winds. Some organisations concerned will arrange additional manpower to take up duty or to stand by, so as to prepare for the adverse weather that the tropical cyclone may bring.
Another situation that warrants a No. 1 Signal is slightly different from the above. This refers to the late stage of the passage of a tropical cyclone, when the No. 1 Signal is issued to replace the Strong Wind Signal No. 3. Such scenario occurs mostly when a tropical cyclone is departing from Hong Kong and local winds have generally subsided below strong force while strong winds are still affecting some offshore waters. On one hand, the No.1 Signal notifies the public that winds over the territory are generally moderating and the threat of tropical cyclone to most people is reducing gradually. Those organisations that have arranged extra manpower may consider standing down. On the other hand, since offshore winds remain strong with high seas and swells over some waters, members of the public should remain on the alert, stay away from the shoreline and avoid engaging in water sports.
Let's take Typhoon Kalmaegi in 2014 as an example (Figure 1). As Kalmaegi came within around 800 kilometres of Hong Kong on 14 September night, the Observatory issued the Standby Signal No. 1 to remind the public to take timely precautions against high winds. Later when Kalmaegi continued to edge closer and local winds gradually strengthened, the Observatory issued Signal No. 3 and Signal No. 8 successively. On the night of 16 September, Kalmaegi departed from Hong Kong and moved into Beibu Wan. Locally, wind strength at many places such as Kai Tak and Chek Lap Kok fell below strong force. However, strong winds still persisted over offshore regions such as Cheung Chau (Figure 2). Signal No. 1 was therefore issued by the Observatory to replace Signal No. 3, indicating that threats posed by Kalmaegi were abating but the public should remain vigilant since offshore winds were still strong.
Figure 1 Track of Typhoon Kalmaegi from 12 to 17 September 2014, across Luzon
and the South China Sea, and into Beibu Wan.
Figure 2 Local wind strength and warning signals on 16 and 17 September 2014. After Signal No. 3
was replaced by Signal No. 1, winds remained strong at Cheung Chau but have
moderated at Kai Tak and Chek Lap Kok.
On occasions, particularly in autumn, monsoon may dominate over Hong Kong after a tropical cyclone departs and weakens. If strong winds continue to prevail, the Observatory will issue the Strong Monsoon Signal instead to keep the public alert of the windy condition.
Public safety is always the Observatory's top priority in considering warning signals. Despite the small size of Hong Kong, wind strength across the territory can still vary greatly. In the future, when a tropical cyclone is departing and people do not experience high winds at where they are, they may hopefully understand why the Observatory still keeps the No. 1 Signal in force for some time.
August and September are normally the peak months of tropical cyclone activity in Hong Kong with an average of about three tropical cyclones (TCs) affecting Hong Kong, necessitating the issuance of tropical cyclone warning signals. However, in 2015, no tropical cyclone warning signal was issued in August and September, the first time since 1946. So what are the reasons behind this "no TC warning" phenomenon?
Less tropical cyclones entering the South China Sea from the western North Pacific
Firstly, except Soudelor and Dujuan, all TCs formed over the western North Pacific (WNP) in August and September this year (Figure 1) recurved to the north and did not enter the South China Sea (SCS). Even for Soudelor and Dujuan which entered the SCS, they weakened after moving across Taiwan and Fujian and did not directly affect Hong Kong. The reason for less TCs from WNP entering the SCS can be mainly attributed to the current El Nino event. Some studies[2,3] suggest that the above normal sea surface temperature over the central and eastern equatorial Pacific in El Nino years displaces the breeding ground of TC in the WNP further east (Figure 2). This increases the chance for TCs to recurve and turn northwards when moving across the WNP, resulting in less TCs entering the SCS.
Figure 1 Tropical cyclone tracks in August and September 2015
Figure 2 Tropical cyclone genesis positions for January - September 2015.
Distribution of the long-term average of tropical cyclone genesis
for January - September is shown in shaded colour.
Less tropical cyclones forming in the South China Sea
Secondly, only one tropical cyclone (Vamco) formed in the SCS in August and September 2015, less than the long-term average of two to three. Vamco moved towards Vietnam and did not directly affect Hong Kong as well. Less TCs forming in the SCS in August and September 2015 was mainly due to the weaker than normal southwesterly airstream over the SCS. This led to less moisture transport and weaker convergence zone in the SCS, which in turn hindered the formation of TCs in the region.
CHOY Chun-wing and WU Man-chi
 Long-term average of 1961 to 2010
 Goh, A. Z.-C. and Chan, J. C. L., 2010: Interannual and interdecadal variations of tropical cyclone activity in the South China Sea. Int. J. Climatol., 30: 827-843
 厄爾尼諾與西北太平洋的熱帶氣旋，陳營華、張文瀾、胡文志、區展衡，發表於第十二屆粵港澳重要天氣研討會，香港，一九九八年一月十五至十七日 (Chinese version only)